Bending process



May 16, 1961 A. GREssE BENDING PRocEss Filed April i6, 1956 UnitedStates PatentO ce BENDING PROCESS Andr Gress, Branges, France Filed Apr.16, 1956, Ser. No. 578,507 Claims priority, application France Apr.19,1955

8 Claims. (Cl. 29157.6)

The present invention relates to a method of bending metal tubes rand itis more especially concerned with bending such tubes to a short radius,the thickness of the tubes being relatively large. By the expressionbending to a short radius, there is meant the bending of a metal tubehaving the following characteristics:

where d is the external diameter of the tube in mm, e is the thicknessof the tube wall in mm., r the theoretical radius in mm. of the iinishedbend, a the nal angle in degrees included between the two limbs of thebend, e being the thickness inmm. of the extrados wall of the bend.

It is known that bending operations of this kind applied to relativelylthick tubes-which is the case for example in the manufacture of tubularcoils-tend to reduce the thickness of the wall on the outside of thebend and to compress and increase the thickness of the wall on the innerside of the bend in the zone 'in which the tube is worked, from whichthere results on the one hand a reduction of the internal diameter ofthe tube, which may in certain cases be such as-to cause a weakening ofthe wall of the tube, and especially a reduction in the internaldiameter of the tube, even extending to the complete closure of thebore.

The present invention is proposed to remedy these drawbacks, and it hasfor its object a sure method which does not produce either cracking orfolding or striction or physical deterioration of the metal of which thetube is constituted at the point at which it is bent, and which reducesthe differences between the elongation and the compression of theopposite -walls of the tube.

The method of bending a metal tube in accordance with the presentinvention consists in subjecting such a tube to a iirst operation ofmoderate bending in the opposite sense to the iinal bending of theelbowed tube to be produced, then bending the said tube at the point ofthe said first bending operation and in the opposite direction to thesaid lirst bending operation, preferably at the same time displacing,towards the internal face of the bend thus formed, the extra thicknessof the compressed wall of the said bend, then bringing up to a hightemperature a part of the internal iiace of the said bend, and thenbringing towards each other the two arms of the said bend and continuingthis latter operation whilst applying a pressure on the internal face ofthe elbow along the bisecting line of the angle of the said elbow and inthe plane of the said bisecting line, in such manner as to pass the benttube into a gauge, the last operation being 'tion which consists inpartly bending the tube 1 to an 2,983,995 Patented May 16, 1961 Theexternal wall of the bend or elbow is preferably cooled during the abovementioned last bending operation.

The present invention willv be explained in more detail below, referencebeing made to the attached drawings which illustrate one form ofembodiment of the application of lthe method, and in which:

Fig. 1 is a diagrammatic view showing the iirst stage of the method ofbending in accordance with the present invention.

Fig. 2 is an identical View of the second stage.

Figs. 3 and 4 are views in cross-section, taken along the line III-JIIIIof Fig. 2, at the beginning and at the end of the second stage of thebending operation, respectively.

Figs, 5 and 6 are plan views showing the beginning and the end of theprocess of bending.

Fig. 7 is a view in cross-section taken along the line VII--VII of Fig.6.

' -In Fig. 1 of the drawings, there is shown a tube designated generallyby the reference No. 1, which is subjected to a irst bending operationof slight extent in the opposite direction to the final bending of theelbow desired. .The tube 1 is bent over a supporting former 2; it can beseen that the compressed part of the wall becomes thickened at 3, whilstthe drawn-ont portion 4 of the w'all of the tube becomes thinner. Thezone 5 is preferably heated so as to facilitate the carry'ing out ofthis operation.

This rst operation is followed by a second manipulaangle of about 110 or120 by supporting the drawn-out zone 4 of Fig. l on the bending sheave6, the part 3 which was previously compressed being then located on theoutside. Thus, this bending carried out in the opposite sense to thefirst bending operation, applies to the .groove of the bending sheave 6oval by hollowing out the bottom of the said groove. Thus, the increasedthickness 7 (Fig. 2) of the intrados 4 is displaced towards the exteriorof the tube and -is received in the hollowedout portion formed in thesheave, whilst the walls of the tube are supported by the buttress anksof this groove. There is shown in Fig. 3 the sheave 6 which has beenoval at'6 and in the groove of which is placed the tube 1 which issupported by the sides 6 of this groove.

In Fig. 4, there is shown the relative position of the roller and thetube; the intrados has penetrated partly into the hollowed-out portion6', and the thickened porI tion 7 has been forced into the hollowedportion 6'.

The bend thus obtained is then heated by applying very f rapid heat tothe part 7 over la limited region (shaded at xoy in Fig. 5). The elbowis then placed on a frame 9 on which two rollers 10, 11 are rotatablymounted on shafts 12, 13 and are retained by bolts 12a, 13a, and twoarms 14, 15 are pivotally mounted on pivots 16, 17 and held in positionby bolts 16a, 17a. On this fname, there is also mounted a punch 18 whichcan be displaced in any known manner (not shown in the drawings) alongthe bisecting line of the elbow.

The elbow having been arranged in this way, the arms 14, 15 are firstmanipulated by bringing them closer to each other as they pivot on theiriaxes, while at the same time the punch moves forward in the directionof the arrow F. When the angle of the elbow has reduced to a certainvalue, for example of the order of about 60, the punch has come incontact with the tube and applies a thrust to it, directed towards thetop of the iigure. This punch has the shape of a fork, .of which thedistances from the bottom 18a to the extremities of the arms 18b, andthe distance apart of the said arms are chosen to correspond to theexternal diameter of the tube being worked so as to prevent it beingcrushed. The combined action of the arms 14, and the punch forces thetube y1 upwards and obliges it to pass between the rollers 10, 11; thetwo limbs of the hairpin bend thus obtained are parallel to each other,the heating having the object of assisting the molecular flow.

If so desired, the operation may be continued or the punch may be freedin the direction opposite to that of the arrow F in order to withdrawthe short-bend tube thus obtained.

In the same way, all subsequent operations of forming in a die and likeoperations may be effected without thereby departing from the scope ofthe present invention.

The device described above is only one example off the embodiment of themethod. All the operations of the method in accordance with the presentinvention can be carried out on a single machine with the object ofmaking the process automatic, using tools designed in accordance withthe nature of the metal of the tubes to be treated.

The operations of bringing the tube arms closer together may beaccompanied by a simultaneous application of cooling to the elbow byanyI known means which are not shown on the drawing.

It will be understood that the application of the method in accordancewith Ithe present invention may only comprise a part of the operationsdescribed, such as for example the operations of bending and folding, orthose of forming bending and folding, or those of bending, folding anddie-forming.

What I claim is:

1. A method of bending a tube of deformable metal to a short radius, ashereinbefore defined, said method comprising the steps of carrying out afirst bending operation through a small angle in a direction opposite tothat of the ultimate bend of the elbowed tube to be produced, so as tothicken the outer wall of said ultimate bend effecting a second bendingoperation on the said tube in the same plane as said rst operation, andin a direction opposite to that of said first bending operation, therebyslightly `reducing the thickness of said thickened outer wall, causingthe thickened portion olf the inner compressed wall of the bend, formedby said second operation, to be displaced toward the inner side of theelbow thus formed by providing a space to receive the displaced metal,heating to a high temperature a zone of the inner face of said elbow,forcing toward each other the straight extremities of said elbowed tubeuntil a certain angle of elbow is reached, subsequently applying a localpressure to the inner face of said elbow in the plane of the angleformed by said elbowed tube and along the bisector thereof, andeffectingthe iinal bending operation by yforcing said elbowed tubebetween at least two gauging members.

2. A method as claimed in claim 1, in which said final bending operationis continued until the said straight extremities of the elbowed tube aresubstantially parallel to each other.

3. A method as claimed in claim 1, in which the said rst bendingoperation of moderate extent is carried out with said tube in the hotstate.

4. A method as claimed in claim 1, in which the extra-thickness of thecompressed wall of said tube, formed during said second bendingoperation, displaced towards the inner side of the said elbow by virtueof an ovality formed in the bottom of the circular groove in the bendingsheave which receives and forms the said tube,

5. A method as claimed in claim l, in which said local pressure appliedto the inner face of the said elbow is created by means of a forkedpunch actulated by suitable means, the forks and body extremity of saidpunch being adapted to fit the external wall of the said tube.

6. A method as claimed in claim 1, in which said final bending operationconsists in forcing said elbowed tube between a plurality of rollersrotatably mounted on a base-plate, the said rollers having circulargrooves formed in their peripheral faces.

7. A method in accordance with claim 1, and comprising the steps ofinwardly bending the straight extremities of said elbowed tube by a pairof arms each pivotally mounted at one of its extremities on a base-plateand shaped to accommodate the outer walls of the said straightextremities along their length, forcing the elbowed portion by saidlocal pressure between the pivoted ends of said sleeves before beingengaged between the said gauging members, and bringing the straightextremities of said elbowed tube towards each other by force applied tosaid sleeves during the final bending and gauging operation.

8. A method as claimed in claim 1, and comprising the further step ofcooling the external surface of said elbow eration.

References Cited in the file of this patent UNITED STATES PATENTS1,463,762 Lente July 3l, 1923 1,775,331 Trainer et al. Sept. 9, 1930FOREIGN PATENTS 680,411 Great Britain oct. 1, 1952 514,786 Belgium Oct.3l, 1952 1,028,236 France Feb. 25, 1953 1,052,124 France Sept, 23, 1953154,073 Australia Nov. l0, 1953

